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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
The Z-Scheme of Electron Transport in Photosynthesis01:34

The Z-Scheme of Electron Transport in Photosynthesis

The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.

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Related Experiment Video

Updated: May 8, 2026

Synthesis and Performance Evaluations of ZnCoS/ZnCdS with Twin Crystal Structure for Multifunctional Redox Photocatalysis in Energy Applications
09:22

Synthesis and Performance Evaluations of ZnCoS/ZnCdS with Twin Crystal Structure for Multifunctional Redox Photocatalysis in Energy Applications

Published on: July 25, 2025

Synergistic Electron-Proton Transfer Over In2O3/CuGa0.5S Z-Scheme Heterojunction for Highly Selective CO2-to-CH4

Jiachen Yang1, Zhenhua Tian1, Yilong Ren1

  • 1International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, China.

Angewandte Chemie (International Ed. in English)
|May 7, 2026
PubMed
Summary

This study presents an engineered Z-scheme heterojunction for efficient solar-driven conversion of carbon dioxide and water into methane. The novel material design enhances charge transfer and proton migration, achieving high methane selectivity and production rates.

Keywords:
CH4Z‐scheme heterojunctionelectron coupled to proton transferphotocatalytic CO2 reduction

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Published on: August 7, 2018

Area of Science:

  • Materials Science
  • Photocatalysis
  • Renewable Energy

Background:

  • Solar-driven conversion of CO2 and H2O to CH4 is crucial for sustainable fuel production.
  • Current methods face challenges in charge separation and proton migration kinetics.

Purpose of the Study:

  • To design an interfacial-engineered Z-scheme heterojunction for enhanced photocatalytic CO2 reduction.
  • To elucidate the mechanism of electron-coupled proton transfer for methane synthesis.

Main Methods:

  • Fabrication of In2O3/CuGa0.5S Z-scheme heterojunction.
  • Characterization using Kelvin probe force microscopy, XANES, XPS, and DRIFTS.
  • Theoretical analysis via DFT calculations.

Main Results:

  • Identified a direct Z-scheme charge-transfer pathway with electron accumulation on CuGa0.5S.
  • Demonstrated enhanced CO2 activation and water dissociation.
  • Achieved a CH4 evolution rate of 319.2 µmol g-1 h-1 with ~100% selectivity.

Conclusions:

  • The In2O3/CuGa0.5S heterojunction effectively synchronizes electron transfer and proton delivery.
  • Synergistic interactions stabilize key intermediates, promoting methane production over H2 evolution.
  • Provides a mechanistic understanding for advancing solar-driven hydrocarbon production.